Work machines frequently have more than one system that can providing a braking force to the work machine. Many work machines have gas or diesel engines that provide a braking force to the work machine when a user provides an input requiring a braking force. The engine is provided select amounts of fuel to power the work machine. The power provided to the work machine from the engine allows the work machine to move on an underlying surface along with providing power to any number of sub-assemblies. The sub-assemblies often include a hydraulic pump that provides hydraulic fluid to hydraulic components of the work machine. The demands on the engine may vary based on the desired speed of the work machine and the needs of the hydraulic components.
Many work machines control the velocity of the work machine by mechanically coupling one or more ground engaging mechanisms to the engine through a transmission. If the work machine requires an increase in velocity, more fuel is supplied to the engine causing it to rotate at a faster speed. In turn, the engine increases the speed of the ground engaging mechanism and the velocity of the work machine is increased.
In one example, when the velocity of a typical work machine needs to be reduced, the fuel provided to the engine is reduced and the engine provides a braking force to the ground engaging mechanism. If the engine braking force is not sufficient to slow the work machine and the velocity of the work machine increases, in a downhill condition for example, the ground engaging mechanism may cause the engine to rotate higher speeds than the engine is designed to handle.
Accordingly, many work machines have a brake system that a user may engage to slow the work machine. The brake system is often a hydraulic system that applies a brake to the transmission or ground engaging mechanism responsive to a user input. In this configuration, the brake system is often engaged while the engine is defueled to facilitate slowing the work machine.
Many hybrid work machines add an electrical motor, generator, or both to help manage the power of the work machine. In the hybrid work machine, the motor and generator, or motor-generator, may be utilized by the work machine to provide a braking force when a decrease in velocity is required. In the hybrid work machine the braking force is applied, in part, by the generator, or motor-generator, converting the mechanical energy generated by the work machine into electrical energy that can be stored or released by the work machine. Often the electrical energy produced by the generator or motor-generator is stored in batteries. However, if too much electrical energy is created as part of the braking function, the generator or motor-generator often uses electronic brake resistors to manage the access electrical energy generated during a braking function.